Method and system for dimming light sources
View Patent ↗Dimming a light source such as a LED over a dimming range (0%-100%) involves adjusting at least one of the intensity (I) and the duty-cycle (DR) of a current flowing through the light source. The dimming range includes at least one portion (L%-H%; 0%-H%) where the light source is fed with a current whose intensity (I) is switched with a given duty cycle (DR) between a non-zero on value and zero, the non-zero on value being a fraction of the rated value (Irated), whereby joint CC and PWM dimming is achieved.
1. A method for powering a light source at selectable brightness levels over a dimming range, the method comprising the steps of:
partitioning the dimming range (0%-100%) into a plurality of portions; and
feeding a current to the light source in dependence upon both: (a) a selected brightness level; and (b) the portion of the dimming range corresponding to the selected brightness level, wherein, for a selected brightness level that is within at least one of the plurality of portions of the dimming range:
(i) the current fed to the light source is a discontinuous, switched current that is switched at a duty cycle between an on value and an off value; and
(ii) the on value is a fraction of a rated current for the light source, and is adjusted in dependence upon the selected brightness level.
2. The method of claim 1 , wherein the off value is substantially equal to zero.
3. The method of claim 1 , wherein the light source includes at least one light emitting diode.
4. The method of claim 1 , wherein:
the step of partitioning includes partitioning the dimming range (0%-100%) into a first portion (0%-L %), a second portion (L %-H %), and a third portion (H %-100%); and
the step of feeding includes:
(i) for a selected brightness level that is within the first portion (0%-L %) of the dimming range, feeding to the light source a continuous, unswitched current having an intensity that is a fraction of a rated current for the light source, wherein the fraction of the rated current is adjusted in dependence upon the selected brightness level;
(ii) for a selected brightness level that is within the second portion (L %-H %) of the dimming range, feeding to the light source a discontinuous, switched current that is switched at a duty cycle between an on value and an off value, wherein: (a) the duty cycle is adjusted in dependence upon the selected brightness level; and (b) the on value is a fraction of the rated current, and is adjusted in dependence upon the selected brightness level; and
(iii) for a selected brightness level that is within the third portion (H %-100%) of the dimming range, feeding to the light source a discontinuous, switched current that is switched at a duty cycle between the rated current and the off value, wherein the duty cycle is adjusted in dependence upon the selected brightness level.
5. The method of claim 4 , wherein the off value is substantially equal to zero.
6. The method of claim 4 , wherein the light source includes at least one light emitting diode.
7. The method of claim 1 , wherein:
the step of partitioning includes partitioning the dimming range into a first portion (0%-H %) and a second portion (H %-100%); and
the step of feeding includes:
(i) for a selected brightness level that is within the first portion (0%-H %) of the dimming range, feeding to the light source a discontinuous, switched current that is switched at a fixed duty cycle between an on value and an off value, wherein: (a) the fixed duty cycle is independent of the selected brightness level; and (b) the on value is a fraction of a rated current for the light source, and is adjusted in dependence upon the selected brightness level; and
(ii) for a selected brightness level that is within the second portion (H %-100%) of the dimming range, feeding to the light source a discontinuous, switched current that is switched at a duty cycle between the rated current and the off value, wherein the duty cycle is adjusted in dependence upon the selected brightness level.
8. The method of claim 7 , wherein the off value is substantially equal to zero.
9. The method of claim 7 , wherein the light source includes at least one light emitting diode.
10. A circuit for powering a light source at selectable brightness levels over a dimming range that is partitioned into a plurality of portions, the circuit comprising:
a processing circuit for defining a selected brightness level for the light source; and
a current generator coupled between the processing circuit and the light source, wherein the current generator is operable to feed a current to the light source in dependence upon both: (a) the selected brightness level; and (b) the portion of the dimming range corresponding to the selected brightness level, wherein, for a selected brightness level that is within at least one of the plurality of portions of the dimming range:
(i) the current fed to the light source is a discontinuous, switched current that is switched at a duty cycle between an on value and an off value; and
(ii) the on value is a fraction of a rated current for the light source, and is adjusted in dependence upon the selected brightness level.
11. The circuit of claim 10 , wherein the off value is substantially equal to zero.
12. The circuit of claim 10 , wherein the light source comprises at least one light emitting diode.
13. The circuit of claim 10 , wherein:
the dimming range (0%-100%) is partitioned into a first portion (0%- L %), a second portion (L % - H %), and a third portion (H %-100%); and
the current generator is further operable:
(i) for a selected brightness level that is within the first portion (0%-L %) of the dimming range, to feed to the light source a continuous, unswitched current having an intensity that is a fraction of a rated current for the light source, wherein the fraction of the rated current is adjusted in dependence upon the selected brightness level;
(ii) for a selected brightness level that is within the second portion (L %-H %) of the dimming range, to feed to the light source a discontinuous, switched current that is switched at a duty cycle between an on value and an off value, wherein:
(a) the duty cycle is adjusted in dependence upon the selected brightness level; and
(b) the on value is a fraction of the rated current, and is adjusted in dependence upon the selected brightness level; and
(iii) for a selected brightness level that is within the third portion (H %-100%) of the dimming range, to feed to the light source a discontinuous, switched current that is switched at a duty cycle between the rated current and the off value, wherein the duty cycle is adjusted in dependence upon the selected brightness level.
14. The method of claim 13 , wherein the off value is substantially equal to zero.
15. The method of claim 13 , wherein the light source includes at least one light emitting diode.
16. The circuit of claim 10 , wherein:
the dimming range is partitioned into a first portion (0%-H %) and a second portion (H %-100%); and
the current generator is further operable:
(i) for a selected brightness level that is within the first portion (0%-H %) of the dimming range, to feed to the light source a discontinuous, switched current that is switched at a fixed duty cycle between an on value and an off value, wherein:
(a) the fixed duty cycle is independent of the selected brightness level; and
(b) the on value is a fraction of a rated current for the light source, and is adjusted in dependence upon the selected brightness level; and
(ii) for a selected brightness level that is within the second portion (H %-100%) of the dimming range, to feed to the light source a discontinuous, switched current that is switched at a duty cycle between the rated current and the off value, wherein the duty cycle is adjusted in dependence upon the selected brightness level.
17. The method of claim 16 , wherein the off value is substantially equal to zero.
18. The method of claim 16 , wherein the light source includes at least one light emitting diode.